Circulating myeloid and plasmacytoid dendritic cells after allergen inhalation in asthmatic subjects
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Background: Dendritic cells are key contributors to initiation and maintenance of T‐cell immunity to inhaled allergen. The purpose of this study was to enumerate the changes in peripheral blood myeloid (mDCs) and plasmacytoid dendritic cells (pDCs), the DCs expressing chemokine receptor 6 (CCR6) and chemokine receptor 7 (CCR7), following diluent and allergen inhalation in asthmatic subjects.Methods: Peripheral blood was obtained from 16 allergic asthmatic subjects before and at 0.5, 1, 2, 3, 4, 6, 24, and 48 h after inhaled diluent and allergen challenges. Dendritic cells were enumerated using flow cytometry.Results: Allergen inhalation significantly reduced mDCs at 6 h (21.3 ± 2.0 vs 15.0 ± 1.8/μl blood; P < 0.05) and 24 h (21.5 ± 3.4 vs 16.4 ± 2.4/μl blood; P < 0.05) after challenge. Circulating pDCs were significantly lower than baseline up to 24 h after both allergen and diluent challenges. There was a significant efflux of CCR6+ mDCs from peripheral blood at 6 h and CCR6+ pDCs at 4 h after allergen challenge, when compared with diluent. There was no difference in the number of circulating CCR7+ mDCs or pDCs after diluent or allergen challenges.Conclusions: Peripheral blood mDCs and CCR6+ mDCs, but not pDCs, are reduced up to 24 h after allergen inhalation. Thus, allergen inhalation causes trafficking of immature CCR6+ DCs from blood into the airway, while that of the trafficking of the mature CCR7+ DCs from the airways into the regional lymph nodes probably occurs through the lymphatic system.
